I have tried to write a very simple addon that would display a very large number on the screen like "1" or "5" , or maybe some very short text like "MOVE" and as I am so new I did not know what frame object to use. I have tried MessageFrame and have used the largest font "GameFontHighlightLarge" but it is still too small and I do not like the way MessageFrame scrolls messages either.

The way I imagine it would be like so:

1) create the widget
2) position the widget - make sure it is transparent to clicks
3) set the text on the widget like "MOVE" which appears in very, very large letters
4) clear the widget so the screen is clean again
5) set some other text maybe
6) size the widget in code so it does not need to be sizeable
7) move the widget to get it away from important screen areas would be nice but can also be done in code

Then you've got to write the relevant code to have the frame show on screen where you want it and when you want it to, of course, but I think you've already got that part figured out (otherwise I can go in more detail and write actual code, rather than just giving pointers.)

Just off the top of my head, but that should be right.

GameFontHighlightLarge isn't a font, it's a template. You want to use f.text:SetFont(fontname, fontsize, fontflags)

GameFontHighlightLarge is a template, yes, and you can use it with :SetFont.

__________________
"You'd be surprised how many people violate this simple principle every day of their lives and try to fit square pegs into round holes, ignoring the clear reality that Things Are As They Are." -Benjamin Hoff, The Tao of Pooh

As an idea I like the DBM's "pull" countdown : great large numbers in the middle of the screen and some small animation or effect, OK, I do not care about the effect, just the numbers/letters on the screen, no need for borders either.

The point being of course, that OP was trying to use GameFontHighlightLarge because they thought it was "the largest font" and would make their text bigger on screen. Which it isn't, it's just a template; font size needs to be set via SetFont to a size that's big enough for their needs. They might not even really need nor care about that template.

IIRC, the largest font size in WoW is hardcoded at 32. Anything more and you'll have to use scaling.

__________________
"You'd be surprised how many people violate this simple principle every day of their lives and try to fit square pegs into round holes, ignoring the clear reality that Things Are As They Are." -Benjamin Hoff, The Tao of Pooh

I'm not sure how true that is, at least not in the current time. Otherwise I wouldn't be able to do this.
(Font size 3000, set with SetFont)

I remember when I was originally messing with this, I used GetFont to get nameplate name font size and re-used it as-is, but it turned out they used some kind of downscaling and the actual font size returned by GetFont was something in the 5 digits, lol. Got a nice surprise when I hit /reload

lua Code:

local f = CreateFrame("frame", "name")

f:SetFrameStrata("HIGH")

f:SetPoint("CENTER", UIParent)

f:SetSize(500, 500)

f.text = f.text or f:CreateFontString(nil, "OVERLAY")

f.text:SetFont("FONTS\\FRIZQT__.TTF", 72, "OUTLINE, MONOCHROME")

f.text:SetPoint("CENTER", UIParent)

f.text:Show()

f.text:SetText("Ta-daa")

f.text:SetVertexColor(1, 1, 1)

(There definitely is a hardcoded limit, but it's much higher than 32 ;p I don't think the screenshot I linked was actually 3000 but I typed in a random large number just to show. At the very least the difference between 32 and 72 is very apparent, and it can even go higher.)